Compensated follow-up system



Feb. 10, 1953 L. c. WEATHERS 2,628,334

COMPENSATED FOLLOW-UP SYSTEM Filed March 14, 1945 7 Sheets-Sheet l [elmd [lg/51 412201:

Feb. 10, 1953 c WEATHERS 2,628,334

COMPENSATED FOLLOW-UP SYSTEM Filed March 14, 1945 7 Sheets-Sheet 2 zma lfw/my Feb. 10, 1953 L. c. WEATHERS COMPENSATED FOLLOW-UP SYSTEM 7 Sheets-Sheet 4 Filed March 14, 1945 my Ru MQ M Feb. 10, 1953 1.. c. WEATHERS COMPENSATED FOLLOVFUP SYSTEM 7 Sheets-Sheet 6 Filed March 14, 1945 eSNg 1953 1.. WEATHERS COMPENSATED FOLLOW-UP SYSTEM 7 Sheets-Sheet '7 Filed March 14, 1945 QJMN VI Iii 1L Patented Feb. 10, 1953 COMPENSATED FOLLOW-UP SYSTEM Leland Clay Weathers, Detroit, Mich., assignor to Vickers, Incorporated, Detroit, Micln, a corporation of Michigan Application March 14, 1945, Serial No. 582,716

( Cl. 318-3i)) 16 Claims.

This invention relates to a compensated follow-up system and more particularly to an electrical remote control system for causing a controlled device at a distance from a transmitter to accurately follow the transmitter even though high friction and inertia loads are imposed upon the receiving end of the system and such loads vary widely due to variations in velocity and acceleration of the controlled device.

The system of the present invention is largely concerned with automatically applying both velocity and acceleration compensation in the system so that the power supplied by the prime mover is varied to compensate for variations in the load on the receiving end of the system so as to materially reduce the lag or lead in the system due to such load variations. The acceleration and velocity compensation may be applied either at the transmitter end of the system or the receiving end or partially at both, and involves the employment of devices which are responsive to velocity and acceleration.

The system of the present invention preferably employs receivers which are directly connected to and rotated by the prime mover driving the load at the receiving end of the system and voltages induced in such receivers when an angle of disagreement exists between the receivers and transmitters are employed to control the prime mover. The present system also includes an arrangement for preventing substantial voltage variations in the signal voltage between the transmitters and receivers due to variations in the number of receivers connected to a transmitter.

In follow-up systems in general, it is difficult to provide a system of remotely controlling rapidly varying loads with accuracy. This is caused in part by the fact that it is impossible to make such systems completely stiff. Dropping speed-load characteristic of electric motors employed to drive the load and leakage in hydraulic systems, if employed, as well as other factors introduce looseness" into the system. For example, the receiving end of the system tends to overshoot the transmitting end and then oscillate about the point of zero angle of disagreement between the receivers and transmitters if inertia loads are imposed on the system. In the present system the velocity and acceleration compensation referred to above provide an extremely stiff system despite dropping speed-load characteristics of the prime movers and at the same time effectively prevents overshooting and end oscillation of the system.

The present invention also includes novel electrical controls for systems employing a hydraulic prime mover for the load at the receiving end of the system, one embodiment of the invention employing a novel form of torque motor for actuating the hydraulic controls.

It is an object of the present invention to provide a new electrical follow-up system embodying velocity compensation to increase the accuracy of the system.

Another object of the invention is to provide an electrical follow-up system in which compensation is made for increased loads due to acceleration of the load.

Another object of the invention is to provide a follow-up system in which compensation for both increased friction loads due to high velocity and inertia loads due to rapid changes in velocity is effected through a device responsive to both velocity and acceleration.

Another object of the invention is to provide a remote control follow-up system in which com pensation for both velocity and acceleration is applied at the transmitting end of the system.

Another object of the invention is to provide a remote control follow-up system in which velocity and acceleration compensation is applied at the receiving end of the system.

Another object of the invention is to provide an electrical remote control follow-up system in which voltages which are functions of acceleration and velocity are produced and employed to modify the control of a prime mover in order to compensate for variations in load on the system due to high velocity and changes in velocities.

Another object of the invention is to provide an improved remote control follow-up system which is capable of controlling loads of large magnitude including both inertia and friction loads while maintaining a small angle of disagreement between the transmitter and receiver and which prevents overshooting or hunting of the system.

A further object of the invention is to provide an improved remote control follow-up system for controlling a hydraulic system driving a load.

Other objects and advantages of the invention will appear in the following description of preferred embodiments thereof shown in the attached drawings of which:

Figure la is a schematic drawing of the transmitting portion of an electric follow-up system in accordance with the present invention;

Figure 1b is a schematic drawing of the re" ceiving portion of the system of Figure 1a;

Figure 2 is a plan view of a compensating device for providing both velocity and acceleration compensation;

Figure 3 is a side elevation of the device in Figure 2;

Figure 4 is an end elevation of the iron structure of a compensating transformer showing the position of coils thereon in dotted lines;

Figure 5 is a fragmentary schematic drawing of a modified control relay useful in the system of the present invention;

Figure 6 is a diagrammatic side elevation of the resistance of the relay of Figure Figure 7 is a view similar to Figure 6 showing a bottom plan View of the device of Figure 6;

Figure 8 is a view similar to Figure 12) showing a modification of the receiving portion of t. e system;

Figure 9 is a view similar to 1b showing a further modification of the receiving portion of the system;

Figure 10a is a view similar to Figure la showing a modification of the transmitting end of the system;

Figure 10b is a view similar to Figure 1b showing a further modification of the receiving portion of the system; and

Figure 11 is a fragmentary diagrammatic view showing in plan the resistor structure of the velocity and acceleration compensating device of Figure 10?).

General description The system of the present invention as exemplified in figures 1n and l b mayinclude a low speed selfpynchronous transmitter a high speed el -s nchronous trans f t r a a velocity and acceleration compensator device shown generally at 22 for driving a compensator transformer 23, the compensator 22 and the transmitters 2t and 23 being driven from a control shaft 2 3,. The complete system may also inelude a low speed control receiver 26 and a high speed control receiver 2? as shown in Figure 1b. The receivers 12.6 and 27 are connected so as to be rotated by a prime mover 23 shown as a hydraulic motor forming a part of a hydraulic system indicated generally at it. A pair of indicating receivers 3! and 32 are also shown in Figure 1a as part of the transmitting portion of th system but such receivers may be positioned in any por- .2.

tion or the system long as they are connected to the transmitters 2i) and 2! respectively. The remaining portions of the system shown in these two figures constitute control circuits and circuits for preventing instability in the system as well as for maintaining a substantially constant differential signal voltage from the transmitters for a given angle of disagreement even though receivers are added to the system or removed from the systern. That is to say, a single transmitter can be employed with a plurality of receivers and a change in the number of receivers connected to a transmitter at a given time has very little effect upon the signal voltages.

Transmitters The transmitters preferably employed in the present invention ar of the dually excited or equal impedance type disclosed in my Patent No. 2,227,42l. Such transmitters are provided with primary windings eXcited from a source of alterhating current and have a quadrature connection which may be substantially short circuited or be closed through an impedance which is substantially equal to the impedance of the exciting circuit. As shown in Figur la the transmitter 29 may have a closed distributed primary winding 33 provided with four equally spaced taps 35, 35, -33 and 31. The primary winding 33 is connected across a source of alternating current 33 through the taps 3d and 3% in series with a winding 39 on a regulator transformer 45. The quadrature connection to the primary winding 33 is connected to the taps 35 and 3'! in series with a winding 52 on the regulator transformer ii and a secondary winding 63 on the stator or" the compensator transformer 23. Similarly the primary winding iz icf the high speed transmitter '2! is provided with taps 4?, 58 and it and is connected across the source 38 through the taps it and 38 in series with a winding 49 on a. regulator transformer 5!. The primary winding as is also provided with a quadrature connection through the taps 41 and it which quadrature connection contains in series therewith, a winding 52 on the regulator transformer'fii and a secondary winding 53 of the compensator transfori 23. The purpose and operation of the regulator transformers ll and 5! as well as the purpose and operation of the compensator transformer 23 will be described in detail hereinafter, it being sufficient to note at present the circuit of theou'adrature'connectionof each of the primary windings of the transmitters and 2! is of substantially the same impedance as the exciting circuit ifor {such primary "winding. This is true since the windings 39 and d2 of the regulator transformer ii associated with the transmitter 2d are of substantially equal impedance and the winding d3 of the compensator transformer 23 is of low impedance. It is to be noted that the primary winding i of the compensator transformer ed with'a short circuited quadrature conne QonE c and that the winding of this transformer is, at the neutral position of the compensator transformer, positioned with respect to the winding 5;} so that the windin s3 is eiiectively short circuited as to alternating voltages by the quadrature connection 56.

Exactly the same conditions are true as o h circuits connected to the primary winding {iii of the transmitter 25. In other words, the windas and 5-2 on the regulator transformer 5! are of substantially equal impedance and the winding 53 or" the compensator transformer 23 is efiect-ively short circuited in the neutral position of the compensator transformer by the quadrature connection 56.

The low speed transmitter 26 is provided with a phase wound secondary winding 5? which has its phases connected through conductors 58, 59 and as with the phases of a phase woun'd'primary winding 62 or the low speed receiver it shown in Figure 112. Similarly the high speed transmitter 23 is provided with a phase wound secondary winding as which has its phases connected through conductors 643,65 and $3 with the respective phases of. a phasewound primary winding 68 of the high speed receiver 2?. It will be apparent that the excitation of the primary winds ing 33 of the transmitter 29 from the source 38 will produce a single phase alternating field in the iron of the transmitter, which field is aligned with the taps in and 31'; of the quadratur connection. This field will induce voltages in the phases of the secondary winding of the trans mitter which voltages will, vary in the different phases of the winding 5? depending upon the angular position of thestator of the transmitter as relativ to the rotor.

The rotor of the high speed transmitter 3: may be rotated through a shaft E39 havin a ear "ii fast thereon which s in turn rotated from the control shaft 2 1- throughafgear :lZmeshing with the gear H. The rotor of the low speed transmitter 26 may be driven through a shaft lehaving a gear 74 fast thereon and meshing with a gear which meshes with a gear 19 on the shaft 69 of the primary Winding 52.

the rotor of the high speed transmitter. It will be apparent that the low speed transmitter is rotated at a much lower speed than the high speed transmitter. A gear 80 which is of half the diameter of the gear I4 is shown as meshing with the gear I4 solely for illustrating the speed of rotation of the ultimate control element, as hereafter explained, although the actual drive from such control element will ordinarily be supplied through a high speed shaft such as shaft 24.

Control receivers As stated above, the control receivers 26 and 27 are provided with phase wound primary windings 82 and 88 respectively which are connected to the secondary windings 51 and 83 respectively of the transmitters and 2|. The phases of the primary windings 82 and 88 of the receivers and 21 are energized by the voltages induced in the corresponding phases of the secondary windings of the transmitters. Currents flow in the primary windings of the receivers to produce single phase alternating fields in the iron of the receivers which vary in angular position with respect to the primary winding of the receivers, depending upon the angular position of the secondary windings of the transmitters with respect to the primary windings thereof. The control receivers 26 and 27 are also provided with angularly disposed secondary windings. Thus the receiver 25 has two secondary windings 8| and 82 arranged at right angles to each other. It will be apparent that voltages will be induced in the windings 8i and 82 by the field in the iron of the receiver 25 caused by currents in the phases of The voltages in the windings 8| and 82 will be equal in magnitude for four angular positions of the rotor with respect to the stator. These voltages will be in phase for two of these positions and 180 out of phase for the other two. In other words, there will be two points of synchronism and two points of false synchronism. An exactly similar condition exists as to the high speed receiver 21. That is to say, voltages will be induced in the secondary windings B3 and E4 of the receiver 21 and these voltages will be equal for four different angular positions with the rotor with respect to the stator and will be either in phase or 180 out of phase.

The voltages induced in the windings on the rotors of the receivers are employed to control the prime mover 28 so as to bring the receivers into a position of synchronism. The system is constructed so that the low speed receiver rotates at half the speed of the ultimate controlled shaft so that either position of synchronism of the low speed receiver establishes a definite angular position of the controlled shaft. The same thing is true with respect to the low speed transmitter 20. In other words, the transmitter 20 rotates at half the speed of the ultimate control shaft so that the controlled shaft corresponds in angular position to the control shaft for either position of true synchronism for the low speed receiver 28. The low speed. transmitter and receiver operate to maintain the controlled shaft within a few degrees of the angular position of the control shaft and the high speed transmitter and receiver take control only within these few degrees to bring the controlled shaft into precise angular agreement with the control shaft.

It will be noted that the rotor of the high speed receiver 27 is directly connected to the prime mover 28 through a rotor shaft 88 having a, gear 81 thereon meshing with a gear 88 on a power shaft 88 driven in any suitable manner, for example, beveled gears BI and 92 from the prime mover 28. The rotor of the low speed receiver may be driven by a rotor shaft 93 having a gear 84 thereon meshing with a gear 96 on a shaft 91 also having a gear 98 meshing with a gear 99 on the rotor shaft 88 of the high speed receiver 21. The gear ratio between the rotor shafts l3 and 89 of the low speed and high speed transmitters respectively is the same as the gear ratio between the shafts 93 and 8B of the low speed and high speed receivers respectively. A gear I00 having half the diameter of gear 94 is shown as meshing with gear 94 solely to illustrate the speed relation of the ultimate controlled shaft, although the drive to such shaft will ordinarily be from the shaft 89 through a separate system of power gearing.

Even though extreme care is taken in constructing all portions of the transmitter and receiver system including these elements themselves, the connections therebetween and any other devices associated therewith to provide perfoot symmetry as far as possible, some phase unbalance will usually be found to exist so that the receivers do not accurately follow the transmitters in all angular positions thereof. It has been found that this condition can be completely corrected by inserting small resistors I00 in one or more of the conductors between the receivers and transmitters. It is more convenient to treat each receiver individually so that these resistors are placed in the individual receiver primary leads. The correct values can easily be determined by connecting variable resistors in the leads to adjust the receivers so that phase unbalance is corrected and then substitute fixed resistors. While such resistors are shown only in the receiver leads, it is entirely possible to cor rect for phase unbalance caused by any device connected to the signal circuit by inserting proper resistors in its leads from the signal circuit.

Low speed receiver control system As stated above voltages induced in the secondary windings of the receivers 28 and 21 are employed to control the prime mover 28 to bring the receivers 26 and 21 into synchronism, i. e., zero angle of disagreement, with the transmitters 20 and 2| respectively. The rotor winding SI of the low speed receiver 28 is connected in series with a winding l0| on a low speed differential control relay I02 and a winding I03 on a saturable reactor I04. Similarly the winding 82 on the receiver 26 is connected in series with a winding I06 on the relay I02 and a winding I01 on a saturable reactor I08. The purpose of the sat-- urable reactors I04 and I08 will be described in detail below but for the present it is apparent that when the voltages in the windings 8I and 82 of the low speed receiver 26 are equal and the reactors I04 and I08 provide equal impedances, the windings IOI and I06 on the relay I02 will be energized to an equal extent. The low speed relay I02 includes U-shaped core members I09 and I II upon which are wound the windings IBI and I06 respectively. The core members I09 and III provide a central circular shaped aperture II2 for loosely receiving a round armature II3. The armature H3 is connected by a member II4 to a spring contact carrying member IIB having one end fixedly secured at I I! and the other end provided with a central contact II8 insulated from the member H6. The spring member H5 maintains the armature H3 in a central position 9 'I control relay I39 havingcore members I M and I42 and a central circular armature I43. The core member MI is provided with a winding I44 connected in series with the winding 83 of the receiver 21 through a winding I48 on a saturable reactor I41. The core member I42 is provided with a winding I48 connected in series with the winding 84 of the receiver 21 through a winding I49 on a saturable reactor I5I. Contrary to the connection of the windings on relay I62, the control windings I44 and I48 on relay I38 are connected so that under conditions of zero angle of disagreement between the receiver 27 and the transmitter 2I the flux in the core members MI and I42 tends to remain in the respective core members and not cross the air gaps between the core members. The core members of the high speed relay I 39 also preferably have their adjacent portions cut away as shown at I56 so that the core members have very little shunting effect on each other. Under these conditions the armature has a strong tendency to remain at one extreme position or the other even when the relay windings I44 and I48 are equally energized. The spring member I52 connected to the armature I 43 through the member I53, however, has sufiicient spring force to maintain the armature I43 close to its central position. As the windings I44 and I46 are energized with alternating current, the result is that the armature I43 constantly vibrates so that the action of the high speed control system is impulsive. That is to say, the entire system constantly vibrates with small amplitude when under control of the high speed receiver so that the effect of static friction is largely eliminated.

Instead of contacts, the armature I43 of the high speed control relay preferably actuates a variable resistance device shown in Figure lb as made up of two carbon piles I 54 and I56 having a central movable member I51 insulated from but actuated by the spring member I52. The carbon pile I54 is connected in parallel with the contacts and the winding I23 of control solenoid I26 and similarly, the carbon pile I56 is connected in parallel with the winding I24 of the control solenoid I26. Thus when there is no engagement between contact H8 and either contact H9 and I2I, the carbon piles I54 and I56 control the energization of the operating windings I23 and I24 of the control solenoid I25. The carbon piles I54 and I56 will, however, always present substantial resistance to flow of current therethrough so that the effect of engagement of contact II 8 with either contact I I 9 and I2I is much greater than the effect of the carbon piles I 54 and I56. This means, that at a predetermined angle of disagreement of the low speed receiver with respect to its transformer, the low speed receiver is in complete control and the high speed receiver is only eilective when the low speed receiver relinquishes control.

When the armature I 43 of the high speed control relay I39 is in its central position, the carbon piles I54 and I56 have equal resistance so that the windings I23 and I24 are equally energized. Movement of the armature I43 in an upward direction decreases the resistance of carbon pile I54 and increases the resistance of carbon pile I58 to shunt a greater amount of current from the coil I23 and decrease the shunting of current from coil I24. This results in a greater energization of coil I 24 than coil I23 to cause the solenoid plunger I34 to move to the right to an extent depending upon the difference in energization of the windings I 23 and I24. Conversely downward movement of armature I43 increases the energization of coil I23 and decreases the energization of coil I24 to cause the solenoid plunger to move to the left.

The circuit for the saturating windings I58 and I59 of the saturable reactors I41 and I5l respectively includes a variable resistor I6I or retardation rheostat, the purpose of which will be more fully described below. Thus a circuit through these windings can be traced from the terminal I21 of the direct current source I29 through winding I56 on reactor I5I, then through resistor SI and winding I58 on reactor I4! back to the other terminal I28 of the direct current source. A roller I62 making contact with the resistor I6I is electrically connected to the inner ends of the control solenoid windings I23 and I24 and also to the central member I 5'! of the carbon piles I54 and I56. The winding I58 on the saturable reactor I41 and the left portion of the resistor I6I are thus connected in parallel with the control solenoid winding I24 and the winding I56 on the saturable reactor I5I and the right portion of the resistor I6I are connected in parallel with the control solenoid winding I23. So long as the roller I62 is maintained in a central position on the resistor I6I, very little current flows through the saturating windings I56 and I59 on the reactors I 4'! and I5I respectively as the resistor I6I has sufficiently high resistance to keep this current at a small value. As hereafter described, the position of roller I62 on resistor I 6| depends upon the velocity and direction of rotation of the prime mover 28 and the retardation rheostat comprising the resistor I6I and contact I62 constitutes a stabilizing means to prevent too rapid movement of control solenoid plunger I34 toward its central position when the system has been traveling at high velocity and the control signal suddenly decreases.

Hydraulic driving system,

While any type of variable speed prime mover can be controlled by the system of the present invention, hydraulic systems have reached a high stage of perfection, providing accurate speed control of driven members. There are several different types of hydraulic systems which can be employed but the majority of them include a variable volume or variable stroke pump I63 driven in any suitable manner, for example, by electric motor I64. The pump I63 drives hydraulic motor 28 which is the prime mover for the controlled member and is ordinarily of the constant stroke type. Both the pump I 63 and the motor 28 may, for example, be of the type disclosed in the patent to Thoma 1,931,969, the motor 28 having a fixed yoke while the pump I 63 has an oscillatable yoke I65 movable by the piston of a, hydraulic cylinder I 66. As disclosed in said patent to Thoma angular movement of the yoke I65 of the pump I63 about its pivot I'II varies the direction of pumping and the stroke of the pump, the stroke increasing from zero as the yoke is moved from its central position shown in Figure 1b. Fluid under pressure may be supplied to the cylinder I 66 from a four way balanced hydraulic control valve diagrammatically shown at I67 having its valve member connected to and movable by the solenoid plunger I34 and provided with a follow-up sleeve I68 actuated by movement of the yoke I65 of the pump I63. A small constant pressure pump I69 may be driven by the motor I64 to supply fluid under pressure to the valve I61 and make up fluid to the main hydraulic system through check valves I76. The hydraulic motor 28 is driven at a speed dependent upon the position of the solenoid plunger 13% as this controls the position of pumpyolre [55; As the plunger its is moved to the right in Fig. it the motor E26 is driven in one direction at a speed dependent upon the position of said plunger and similarly if the plunger its is moved to the left, the motor 28 is driven in the opposite direction at a speed dependent upon the position of the plunger I3 1. The roller E62 of the retardation rheostat is mechanically connected to the pump yoke 565. Since the position of the yoke It5 of the pump is determined by the speed anddirection of the motor 2-3, the position of the roller I62 on the resistor if is a direct function of the velocity of the driven or controlled member.

Compensator The compensator 22' shown diagrammatically. in Figure la and in greater detail in Figures 2 and 3 may include a disc H2 of electrically conducting material carried by a shaft H3 journaled in a pivoted member II -i which in turn is pivotally mounted on a shaft lit positioned in a standard if! shown in Figures 2 and 3. The shaft I73 for the disc 5'52 carries a small gear if? meshing withthe gear ii on the rotor shaft 69 of the high speed receiver. The shaft lit for the pivoted member lid is mounted concentric with the shaft t9 so that the pivoted member PM may oscillate about the center of shaft ll'e while retaining the gear I'll in meshing relationship with the gear ii. The pivoted member carries a magnet H8 which-has its poles positioned on opposite sides of the disc-member H2 so as. to constitute a magnetic drag for the disc. The pivoted member li t is provided at one end with a segmental gear H9 which meshes witha gear it! on the rotor shaft 32 of the compensator transformer 23'. The pivoted member may be provided with a counterweight l83 for the disc I72 and associated gearing as well as for the segmental gear ["53 so that the i compensator may be mounted in any position, for example, the horizontal. position shown in Figure 3.

It will be apparent that when the shaft of the high speed receiver 2! is being rotated, it will drive the disc I72 through the gears ii and Hi". Since the magnet H3 exerts a magnetic dra on the disc N2, the pivoted member l-"M tends to be carried around by the gear '55 actin through the gear IT? and the shaft H3. The force tending tomove the pivoted member lit will be a direct function of the speed of rotation of the disc 112, that is a direct function of the speed of rotation of the control member. This force tend to rotate the rotor shaft I32 of the compensator transformer 23 throughthe segmental gear H9 and the gear Hit. The compensator transformer resists such rotation as hereafter described but for any constant speed of the control shaft 26, the rotor of the compensator transformer 23 is rotated to an angle which is substantially proportional to the speed of the control shaft and the direction of which depends upon the direction of rotation of the shaft This action of the compensator provides for v locity compensation, i. e., changes in friction loads due to changes in velocity, also hereafter explained.

The compensator 22 also provide acceleration compensation to compensate for varied loads due to inertia of the controlled members. The disc H2 in addition tov being made of electrically conductive material also hasv a relatively large moment. of inertia. This means that the disc iii resists sudden. changes in its speed of rotation sothat a sudden increase inthe' speed ofithe shaft es and gear; Tl causesithe pivoted member [is to move furtherin direction of. the rotation of the gear '11 Conversely a sudden slowing down of the gear ll will cause the pivoted member [it to move in av direction. opposite to the direction of the rotation of the gear II. Thus a. change in speed of rotation of the gear ll introduces an acceleration compensationwhich may add to or subtract from the velocity compensation de scribed above. The compensator above described isessentially a mechanical differential having an input shaft constituting. the control shaft 25, an output shaft constituting the compensator shaft 182. and an intermediate shaft having a weighted disc thereon also subjected to a drag such as a magnetic drag whichi's proportioned to the speed of rotation of the intermediate shaft.

compensator transformer The compensator transformer 23 is employed to introduce voltages into'the primary windings of the transmitters 2G and 25 which have the ct of rotating the fields in the iron of the tran mitters. The primary winding of. the isator transformer is preferably a closed win. mg excited. in one axis from the alternating current source This excitation produces a single phase alternating field in the iron of the compensated transformer'which cuts'the conductors of the compensating, windings i3 and 53 which are connected to theprimary windings 33 and as res actively of the'transmitters. As long as this is in. quadrature to the windings t3 53', i". e., the. compensator is in neutral position, no resultant voltages are induced in these e. If the. rotor of the compens' transformer is rotated so as to occupy a position at an angle from this. neutral position resulta voltages are induced in the windings G3 and and these voltages are introduced in the quadrature axis ofthe windings 33' and. it respectively of the transmitters. Quadrature currents then flow into. windings 33' and it to produce fields at right angles to the main fields in the iron of the transmitters Ed: and 25 which have a magnitude substantially proportional to the angular displacement of the rotor of. the compensating transformer 23 from its neutral position. The effect is to rotate the fields in the transmitters 2t 2i to a degree which is substantially proportional to the velocity of the high speed transmit er 2 l or the acceleration thereof or both. correctly connecting the windings t3 of the compensating transformer to the windings and 2 5 respectively of the transmitters, the rotation of the fields in the transmitters and 2t gives the same effect as an additional rotation of the rotors of the transmitters themselves. is to say, a given speed of rotation of the shaft s of the high speed transmitter produces the effect of a lead of both transmitters. The thing is true of an. acceleration in given direction whereas a deceleration produce effect of a lag of the transmitters. This lfag transmitted to the receivers 25 and that the controlled mechanism associated therewith applies increased power to the controlled .oember proportional to the speed of rotation of system and to a positive acceleration of all e power applied to the. controlled member.

Because of leakage reactance the secondary v itage of the compensator transformer tends to be slightly out of phase with the primary voltage;

but the secondary voltage of the compensator transformer should be exactly in phase witli the excitation voltage of the transmitters which is the same as the primary voltage of the compensator transformer. By inserting a resistor I83 in the primary circuit of the correct value, the secondary voltage of the compensator transformer can be brought into phase with the excitation voltage for the transmitters.

There are two factors tending to return the rotor of the compensator transformer to its neutral position in which no voltages are induced in the windings 53 and 53. One of these is the motor action caused by currents flowing in the windings I33 and 53 by reason of the closure of these windings through the windings 33 and 44 respectively of the transmitters. The other is a result of the iron structure of the compensator transformer, this iron structure is shown diagrammatically in Figure 4 and inaudes a stator structure ids having a plurality of substantially closed slots 5% in opposite portions thereof, the slots approaching quite close to the periphery of the stator structure to provide relatively thin iron sections at iti. The rotor structure I86 preferably has four equally spaced substantially closed slots. The four coils of the closed rotor winding st are indicated by the dotted lines connecting the slots I353. The position of the stator windings 33 and 53 are shown by the dotted lines connecting the stator slots I36. Preferably both windings 33 and 53 are positioned in all of the slots of the stator but the winding 43 for the low speed transmitter will ordinarily have a lesser number of turns than winding 53 since the angle of disagreement is always greater when the low speed transmitter is in control than is the case when the high speed transmitter is in control.

When the primary windings 54 are excited as shown in Figure 1a, a single phase alternating field is set up in the iron of the compensating transformer and the rotor seeks a position of minimum reluctance for the magnetic field. This position of minimum reluctance of the field is indicated by double ended arrow E83 (Fig. i) as in this position the majority of the flux has to traverse only two of the thin sections I81 in its complete circuit whereas in a position at right angles to the arrow I 93 the flux must necessarily traverse at least four of the thin sections I81 in its complete circuit. The result is that there is a restoring force resisting rotation of the rotor from its neutral position shown in Figures 4 and la and no springs are required for returning the compensating transformer to its neutral position when the force imparted thereto from the compensator decreases to zero.

Exciting transformers The system thus far described is completely operable to produce accurate fol1ow-up action.

The three wire receivers 26 and 2?, however, constitute an inductive load on the transmitters 211 and respectively at all times. That is to say, the transmitters must furnish excitation current or the receivers resulting in a very low power factor in the system. This is desirably overcome Jy employing static condensers to furnish at least a portion of the exciting current. Since the voltages across the conductors between the transmitters and receivers are relatively low, extremely large capacity condensers would have to be employed if the condensers were directly connected to such conductors. It is, therefore, desirable to employ step-up transformers but care must be taken to prevent phase unbalance due to dif ferences in impedance in the windings of such transformers. For this purpose a balanced three phase transformer has been developed, one of which I94 is shown connected to the conductors 64, 65 and 66, between the high speed transmitter 2| and receiver 21. Transformer I94 has a laminated Y-shaped inner core member I96 hav ing three equal legs extending at angles of 120 to each other. This inner core member I96 is surrounded by a laminated ring-shaped magnetic member I91. The phase windings I93 are shown as being positioned on the individual legs of the inner core I96 and are further shown as consti tuting Y-connected auto transformer windings. Condensers I are shown as being connected across the high voltage terminals of the auto transformer windings. If the condensers 95 all have the same capacity and the windings I98 are similar, phase unbalance due to unequal magnetic circuits in the transformer is substantially eliminated and can be further corrected by resistors in the leads, if necessary. An exactly similar transformer I94 and associated circuit can be connected to the conductors 58, 59 and 60 con necting the low speed transmitter 2E} and receiver 26 and the elements of this transformer and associated circuit have been given the same reference numerals. With this arrangement the condensers I99 can have relatively small capacity if they are capable of withstanding high voltages. A desirable adjustment of the system is to provide condensers I59 of sufficient capacity to furnish half of the exciting current for the system. under average load conditions, the remainder of the exciting current being furnished from the source 38.

Regulator transformers One of the advantages of the present system is that a large number of receivers can be controlled from a single transmitter and that the number of receivers connected to a given transmitter can be varied during operation of the system Without disturbing the accurateness of the follow-up action. In the system thus far described, however, adding additional receivers will decrease the control voltage from a transmitter and removing receivers will increase the control voltage. The regulator transformers All and 5i shown in Figure 1c can be employed in ccniunction with the static condenser circuits just described to maintain a substantially constant signal voltage in the system as receivers are connected or disconnected from a transmitter. Transformer M has, in addition to the windings 39 and 42 in the direct and quadrature circuits respectively of the transmitter primary windings 33, a third winding 21H on a central leg of the core. The winding MI is preferably of a greater number of turns than the windings 39 and so that the transformer LII constitutes a step up transformer. High voltage condenser 282 is connected across the terminais of the winding 2s: and since this winding is symmetrically disposed with respect to windings 3i} and 22 it does not disturb the substantially equal impedance relation of the circuits including the latter mentioned windings.

The voltage drop across the primary winding 39 of the transformer AI will lead the current by approximately ninety degrees, there being a small in-phase component to supply the losses. At no load, i. e., no receivers connected to the transmitter 20, the transmitter circuit will be drawing a leading current from the source 38 because oi the exciting condensers ice in the secondarv circuit of the transmitter. Thus, the voltage drop in the primary winding 55 of the regulator transiormer will be practically in phase le-position to the line voltage and the voltage t the transmitters will be reduced. As load applied, that as more receivers are connected to, the transmitter a, condition will eventually be reached where the current, to the transmitters is in phase with the voltage. The our-rent will then have its, minimum value; the voltage drop across the regulators will also be a minimum. As more. load is applied, the current to te transmitter will lag the voltage and the voltage drop across the regulator is in such a direction as to to the line voltage. Thus, the secondary or signal voltage of, the transmitter will remain practically constant regardless of load. core the regulator transformer is designed so will be just saturated at full. load. Then, if the transmitter should become overloaded, the voltage across the condenser 252-, connected to the secondary of the regulator transformer, will not become excessive. The regulator transforner for the high speed transmitter is also provide with a secondary winding res and condenser 2t and operates in conjunction with the condensers 39 in the secondary of the transmitter 2i in exactly the same manner as the transformer ii to maintain the signal voltage in the secondary of the transmitter 21 substantially constant irrespective of the load on the. transmitter.

Indzcating receivers The indicating receivers 3i and 32 are preferably of the general type also shown in my Patent No. 2,227,471. Thus the indicating receiver 3i provided with a phase wound primary winding zee connected to the phase wound winding 5? of the transmitter 25 and a short circuited second ary winding 2!! having two coils positioned at right angles to each other and having their end tell. inals interconnected. The indicating receiver 32 is entirely similar to the, indicatin receiver 3i and has its phase wound primary winding 2i2 connected to the phase wound winding 53 of the high speed transmitter 2! and a short circuited secondary winding 2J3 entirely similar to the winding 2i I. of the indicating receiver 35. it see indicating receivers have two points of synchronism as is the case with the power receivers 26 and 27. By graduating the dials 2M 2 it of the indicating receivers so that each half of the dial has a scale from zero to 369 the indicating receivers indicate the correct angular position of the ultimate control member or controlled member.

Such indicator receivers can be employed at any place in the system sov long as they are con-, nected to transmitters in the same manner in Figure la. Such receivers also constitute an inductive load on the transmitters as all of the exciting current therefor is supplied either from the transmitters or the static condenser ci cults above described. In this connection it is possible to provide a static condenser circuit for each receiver to be connected and disconnected from the system along with the receiver, in which case the system can be made to operate at unity power factor or any desired power factor and the signal voltage from the transmitters will remain cone stant except for resistance voltage "drops even if the regulator transformers ll and El and their associated, condensers are eliminated from the system. This can be done by merely short cirl. the receiver of Figures iii and lb The shown in 1a and 1b intended to provide accurate follow-up operation of a controlled shaft ito (Figure lb) from a remote control shaft 3% (Figure la) even though the controlled sha ft iilil is connected to moving devices of large mass requiring movement at high velocity. For example, the shaft 2% connected through a gear train to control shaft 58 may be the out-put shaft of a. gun mount control computer and the shaft til connected through a gear train to controlled shaft lilo drive a heavy gun mount for firing at rapidly moving targets. It is to be noted that the transmitters and Bi are rigidly mechanically connected to the shaft 24 and the re eivers 2d and 23" are rigidly mechanically connected to the shaft til. Actual driving of the shaft 35 is accomplished through the prime mover fit under control of voltages induced in secondary windings of the receivers 25 when there is an angle of disagreement between the transmitters 2i) and 2! and receivers 25 and 27 respectively.

In driving gun mounts or other similar devices, there are. three different types of loads which must be considered. One of these is substantially independent of velocity or acceleration, such as a load due to unbalance of the mount, windage thereon, etc. Such a load can not be compensated for in the follow-up system itself and in any system which has a degree of looseness, as is true of all systems, this type of load will cause a lag or lead of the driven or control member behind the driving or control member. By eliminating such loads as ar possible and providing a prime mover of a mate power this lag or lead can be held to a minirnu type of load is the friction load v stantialiy proportional to velocity Oi mo of the controlled member and will tend to ca se a lag. Any lag due to type oi c substantially eliminated by velocity compensation in accordance with the present invention. A third type or" load is inertia load due to rapid changes in velocity mass and may either cause a lag or lead depen upon whether the driven mass is being accelerated or deceleratedl Any lag or lead due to this type of load can also be substantially eliminated acceleration compensation in accordance wit present invention. Substantial lags or leads due to friction and tia enables the controlled member to much more accurately follow the control member.

The friction load on the pr me stantialiy proportional to the speed of f the controlled member. Increase cause a lag of the controlled member belzin the control member. Under these conditions the magnetic drag on the disc iii the compensator 22 by reason of the magnet iii! causes the pivoted member lit to advance in the di rection of rotation of the gear ii to rotate the rotor of the compensating transformer t an angular position causing voltages to induced in the stator windings, es and in turn causing currents to flow in t rature axis of the primary windings 33 and 4t of the transmitters and 2|. These currents effectively rotate the fields in the transmitters to produce an effective lead of the transmitters. This lead is reflected by a rotation of the fields in the receivers 26 and 21 so that voltages are induced in the secondary windings of the receivers which cause whichever control relay I62 and I39 is in control to cause movement of the control solenoid plunger I34 in a direction to increase the speed or power of the prime mover it. That is to say, the control plunger I34 moves a greater distance in the required direction when under control of the high speed relay I39 and remains in its out of center position for a longer period of time when under control of either re ceiver, than would be the case if no velocity compensation where employed. The greater the velocity, the greater this compensation so that increased power supplied to the prime mover 2S effectively compensates for increased friction load under high speed operating conditions.

If the velocity of the system is suddenly increased by increased speed of rotation of the control shaft 24, the inertia of the disc I12 also causes the pivoted member I14 to be carried around by the gear II so as to add to the velocity compensation effect just described. The effect is to supply more power to the prime mover 28 than would be the case if no acceleration compensation were introduced into the system. The controlled shaft, therefore, more closely follows the control shaft. If the speed of rotation of the system is suddenly decreased the inertia of the disc I12 causes the pivoted member to move in a direction opposite the direction of the rotation of the gear 1! so that a negative acceleration compensation is introduced into the system. This negative acceleration compensation subtracts from the velocity compensation above discussed so that less power is supplied to the prime mover 26 than would he the case if the negative acceleration were not introduced into the system. This also enables the controlled shaft 89 to more closely follow the control shaft 24.

It will be apparent that velocity compensation drops to zero when the velocity of the system is zero but that acceleration compensation may even be a maximum at zero velocity whenthe system is rapidly slowing down and reversing the direction of its rotation. The system is entirely stable when operating at uniform velocity or when accelerating. It has been found, however, that under conditions of deceleration the control tends to stop the controlled shaft at too rapid a rate this fact being largely due to the necessary employment of a centering spring in the control solenoid I26. This is also true of systems which do not have the velocity and acceleration compensation arrangement of the present invention although the acceleration compensation of the present system contributes to this result since it also tends to supply a stopping torque to the control shaft at a greater rate than would be the case if the acceleration compensation were eliminated. The centering spring I36 of the control solenoid I stores up potential energy under constant velocity or acceleration conditions of the system. energy is quickly returned to the system whenever differences in the control voltages in the receivers 26 and 21 decrease, thus tending to decelerate the control shaft at too rapid a rate. In the system shown in Figure lb the resistor it! and contact member I62 functions as a 18 stabilizing means to prevent the too rapid movement of the plunger I34 to its central position when the system starts to decelerate.

The resistor I5! is a voltage divider and has its central contact I62 connected to the volume control of the pump I63. When the load has been traveling at high speed the yoke I65 of the pump is positioned at an angle to its body so that the contact I62 is moved to a position near the end of the resistor it. For example if the contact I 62 is near the left end of resistor I6 I, the energization of winding I23 of the control solenoid I26 is increased over that of winding I24 since winding 6'24 is shunted to a greater extent than coil I23. This holds solenoid core I34 to the left, even though no angle of disagreement exists between the transmitter 2I and the receiver 21. This introduces velocity compensation at the receiver and may cause the system to become unstable. The saturable reactors I41 and I5I are, however, connected to oppose the action of the resistor 56 i. That is to say when the contact I62 is to the left, the winding I58 of reactor I41 carries more current than the winding I59 of reactor I5I. This reduces the impedance in the circuit including relay winding I 44 and increases the impedance in the circuit including relay winding I48. Even though the voltages in receiver winding 83 and 84 are substantially equal, the armature I43 of relay I39 tends to move upwardly because of greater energization of winding I44 than winding I48 so that this action tends to energize control solenoid winding I24 to a greater extent than solenoid winding E23 so as to tend to draw control solenoid plunger I34 to the right. Thus, if the velocity of the system should suddenly change, resistor ISI introduces velocity compensation but the reactors I41 and I5I introduce a counter change to partially balance action of resistor ISI. This completely eliminates unstability. The action of the reactors I41 and IEI is, however, somewhat less than that of the resistors I6I so that resistor I6I always exercises some measure of control. The result is that when the load is being driven at high speed and the control voltage from the receiver 21 suddenly drops to zero, the solenoid plunger I34 is prevented from suddenly moving backward from its central position. Too rapid stopping of the controlled member is thus prevented. The saturable reactors are designed so that the retardation rheostat I6I can never over-control. That is to say, that the receiver 21 always exercises some control. If the load is operating at high velocity and the control shaft slows down, the controlled shaft may over haul and pass the control shaft so that the angle of disagreement will be reversed. The retardation rheostat I62, however, prevents sudden reversal of the position of the solenoid plunger I34. The controlled member will, however, start to slow down and contact I62 of resistor I61 moves back toward its central position. The solenoid plunger I34 will be retarded in its return to its central position and during this time the load will be lagging the control shaft but this error is cancelled out by the velocity compensation introduced in the transmitter.

The control action of the low speed receiver 26 and differential relay IE2 is much greater than that of either the high speed relay I39 or the retardation rheostat I6I. This is true as both of the latter devices always leave substantial resistance shunting coils I23 and I24 of the control solenoid I26. The contacts H8, H9 and I2I of the low speed relay, however, substantially completely short circuit cheer the other of the windings 523 or $2 3 except as this action is modified by the resistor I22. The extent of movement of the control solenoid plunger I3 1 and thus the maximum speed of the controlled member when under control of the low speed receiver can be predetermined by the value of resistor I22. The lowspeed relay control system is adjusted so that the low speed relay does not engage its contact H5 with either contact Iis or I2! until the low speed receiver 25 has a predetermined angle of disagreement with its transmitter. The high speed receiver must have an angle of somewhat less than 90 with its transmitter when the low speed receiver takescr relinquishes control. example, in system which the-high speed receiver travels at 3% times the speed of the low speed receiver, the high speed receivercan only be depended upon to bring the controlled shaft into synchronism with the control shaft within an angle somewhat less than 2 /2" on either side of zero angle of disagreement for the low speed receiver or 5 referred to the shaft of the ultimate controlled zneinber. adjusting the speed control system so that the low speed relay 522 closes or opens its contacts at an angle of approximately 2-on either side of zero angle of disagreement cf the low speed receiver, the high speed receiver takes control only within this small total angle of 4 closest to zero angle of disagreement for the 11:.

low speed receiver.-

2 Receiving system 3 Figure 8 The receiving system of Figure 8 is similar in many respects to the receiving system of Figure 1b. The gear connections between the low speed and high speed receivers and the major portion of'the hydraulic system has been omitted in Figure 8 to avoid duplication, as these elements may be'the same as those shown in Figure 122. When ure la. The coils 8i and 82 of the secondary winding of the low speed receiver 26 are connecte'd-to windings IIiI and I86 respectively of a low speed control relay IE2 through windings I03 and II]? respectivelyof saturable reactors ms and I98 respectively in exactly the same manner as Figure 1b. Thelow speed receiver 25 and the'low speed control relay operate in the same manner as the corresponding elements of Figure 1b; The high speed control relay I39 also has its-windings I34 and I43 connected to the secondary windings 83 and 84 of the high speed receiver 27 through windings I46 and I49 respectivelyof reactors It? and II respectively in the same manner as in Figure 1b.

Instead of employing a control solenoid I26 as in Figure 1b, the system of Figure 8 employs a direct current torque motor 2II controlled by the relays I02 and I39. This torque motor is providedwith a rotor winding 2I8 comprising four coils 2I9, 220, 22I and 222 and a stator winding 223. The torque motor2I'I may have an iron structure the same as that shown in Figure 4 and described with reference to the compensating transformer 23 of Figure 1a. The individual coils 2'I9, 220, 22I and 222 of the rotor winding For may be positioned in the slots I89 of the rotor iron of Figure 4' as shown by the dotted lines connectingthese slots while the stator winding 223 may be positioned in the slots I86 of the'stator iron in a manner similar to that shown by the dotted lines connectingthe slots in Figure 4. The rotor winding 2 I 8 of thetorque motor 2 I 'I may. be energized in one axis from the direct current source 223 shown as comprising a bridge rectifier circuit 226 connected to the secondary winding 221 of a transformer 228 having a primary winding 229 connected to an alternating cur.- rent source 23I. The winding2I8 of the torque motor 2I'I has a short circuit connection 232 in the quadrature axis. As explained with reference to the'compensating transformer 23 of Eigure'la, the'genergization of the rotor winding 2m: causes the rotorto'seek a positionof. minimum reluctance such that'the held through the rotor is aligned in the direction of the double arrow I93 of Figure 4 and in'the "absence of, any energize"- tion of winding 22.3 the rotor returns to this position. When the relays Hi2 and I39 have their armatures' I I3 and l i3'respectively in'the central position, the winding 22.3 of the torque motor is not energized. This winding has one terminal connected to a center tap 233 on the secondary winding 227 of the'transformer 228 and its other terminal connected to the central member I5'I-oi the carbon piles I54 and I58 controlled'by relay I39 and the central contact I I8 actuatedby relay I02. The upper and lower contacts H9 and. I2I ofrelay'IflZ areconnected across the direct current source 226 in parallel with the carbon piles I54 and I56 of the high speed relay I39 in series with saturating winding I35 and liii respectively of reactors I08 and I64 respectively. It is ap} parent that the winding 223 has no voltage impressed there across when the central member I51 of the relay I39 is in its central position so that the carbon piles Itdand I53 have the same resistance and thecontact I I8 of relay I62 is out of engagement with cont'actsl I9 and IZI When the'voltage induced'in the windingstt and 84 of high speed receiver 27 becomes unequal, the armature I43 of relay I39 moves from its center position to compress one of the carbon piles I54 and I55. This causes energization of the winding 223 of torque motor in one direction or the other depending'upon whichcarbon pile is compressed. The field produced in the iron of the torque motor 2 I I by energization of the winding 223 is at right angles to the field produced by the winding 2| 8 so that the rotor tends to rotate in a direction to align the fields an amount which is substantially proportional to the energization of winding 223; Similarly differential energization of low speed relay I92 from its receiver 26 causes the armature I I3 thereof to move contact II8 into engagement with either contact H9 or I2I. Engagement with one of these contacts applies the full voltage of the direct current source 224 except for the drop in resistor I 22 across thewinding 223, the direction of the voltage thus applied dependirig upon which contact IIQor I2I is engaged by contact H 8. Rotation of the rotor of torque motor 2|? actuates the hydraulic control valve IS'I which may be the same as the hydraulic control valve I6? shown in Figure 11) by means of a crank 236 and link 23?. The effective control of low speed relay I02 is much greater than that of high speed relay I39 so that engagement of contact H8 with either contact I I9 or I2I causes the low speed'system to take control.

The saturating windings I31 and I36 of saturable reactors I 04 and I98 respectively are connected in series with the contacts I2! and HS respectively and operate in the same manner as the similar windings on the saturable reactors of Figure 11:. That is to say, current flow through winding I36 due to engagement between contacts II 8 and lie when the armature II 3 of relay I62 is in its uppermost position, reduces the impedance of the circuit including coil 82 of the low speed receiver 26, windings ID! of the saturable reactor I68 and relay winding I66 so that the energization of winding I66 is increased to assist in returning armature H3 to its central position. The saturable reactors I41 and Hit associated. with high speed relay I39 operate in substantially th same manner as the similar reactors discussed. with reference to Figure 1b. The saturating windings 238 and 239 thereof, however, are energized in somewhat different manner. Both windings 238 and 239 are connected across the terminals of the winding 223 of the torque motor 2 in series with unidirectional conducting devices MI and 242 respectively. When the winding 223 is energized in one direction the current flows through saturable winding 238 on reactor i4? and when winding 223 is energized in the opposite direction the current flows through winding 239 on reactor I5i. The

connections are such that the saturable reactors u I47 and I5I reduce the impedance in the wind ing I44 or I46 which has the lesser voltage impressed thereacross from the windings 83 and 84 of the high speed receiver 2?. Since the rotor of torque motor 2 l! is not returned by spring tension but returns to neutral position by magnetic attraction at a controlled rate set by the inertia of the rotor as well as the rate of decrease of energization of the winding 223, no retardation rheostat IBI, such as shown in Figure 1b, is required to prevent too sudden stopping of the sys" tern of Figure 8.

The operation oi the system of Figure 8 is substantially the same as that of Figure lb except that a torque motor has been substituted for the control solenoid of Figure 1b, and retardation resistor I6I of Figure ID has been omitted. and the saturating winding of the saturable reactors i4i and I5! have their saturating winding energized under control of relay I39 and have unidirectional current devices in series therewith in order to enable their proper energization to assist in returning armature I43 of relay I 39 to its central position. As explained with reference to Figure 1b the action of the low speed relay I62 overcomes any action of high speed relay I36 to take control whenever contact H8 engages contact H9 or i2I. The system is adjusted so that the low speed relay I02 takes control at a predetermined maximum angle of disagreement, for example, 2 oi the low speed receiver on either side of zero angle of disagreement thereof in a system in which the high speed receiver and transmitter rotates at 36 times the speed of the low speed receiver and transmitter.

Receiving system of Figure 9 The receiving system of Figure 9 is essentially similar to the receiving system of Figure 8 in that the torque motor 2 I? is employed to actuate the control valve of the hydraulic system. It differs from the system of Figure 8 in that an amplifying system 243 is employed to increase the power delivered to the control winding 223 or the torque motor ZIT. This amplifying sys-- tem includes a pair of gas filled grid controlled tubes 244 and 246 connected for halfway rec-- tification in opposite directions under control of phase shifting circuits for controlling current flow through the tubes. The tubes 244 and 246 are each connected in a series circuit with the winding 223 across a'source 241 of alternating current. The control grids 248 and 249 of the tubes 244 and 24.6 respectively are normally supplied with alternating current voltage out of phase with the respective anode voltages of the tubes so that no current flows through either of the tubes under such normal conditions. With respect to the tube, 244, this is accomplished by a center tapped secondary winding 25I on a transformer 252 having itsprimary 253 across the source 24?. The control grid 248 is connected to the common terminal 254-between a condenser 255 and a carbon pile resistor 256 forming a series circuit across the end terminals of the transformer secondary winding 25I, the center tap of this winding being connected to the cathode of the tube 244. When the resistance of carbon pile 256 is large compared to the capacitive reactance of condenser 255 the voltage impressed on the grid 248 of the tube 244 is substantially 180 out of phase with the anode voltage thereof. When the resistance of the carbon pile 256 is lowered the phase of the grid voltage shifts toward an in phase rela tion with the anode voltage so that the tube 244 becomes conductive, the conductivity of the type depending upon the degree of phase shift. A similar circuit involving center tapped secondary winding 256 on the transformer 252, condenser 259 and carbon pile 26I is provided for phase shifting of the voltage applied to the control grid 249 of tube 246.

The carbon piles 256 and 26I are associated with the spring member I52 of the high speed; relay I 39 so that movement of the armature I43 thereof away from a central position compresses. one or the other of carbon piles 256 or 26I toreduce its resistance and thus render conductingone of the tubes 244 or 246 respectively. This action energizes winding 223 of torque motor 2 I! in one direction or the other depending upon which tube 244 or 246 is rendered conductive. The primary winding 2I8 of torque motor 2|? is energized with direct current by means of a bridge rectifier 263 connected across the source '24! and the torque motor operates in exactly the same manner as torque motor 2 I! of Figure 8 except amplified power is supplied thereto from the control system.

The operating windings IUI and I66 of the low speed relay I62 of Figure 9 are connected in exactly the same manner as the similar windings relay I62 of Figure 8. Contacts 266 and 261 of low speed relay I02 are connected in parallel with carbon pile 256 of high speed relay I36 and contacts 268 and 269 of low speed relay I02 are con nected in parallel with carbon pile 26I of high speed relay I39. It will be apparent that engagement of contact 261 with contact 266 will shift the grid voltage of tube 244 completely into phase with the anode voltage thereof to render this tube completely conductive and similarly engagements of contacts 268 and 269 of low speed relay I02 will shift the grid voltage of tube 246 into phase with the anode voltage to render this tube completely conductive. Again, the low speed relay I62 takes control at a predetermined angle of disagreement of the low speed receiver with the low speed transmitter as the carbon piles 26I and 256 associated with the high speed receiver always have substantial resistance even when the armature access-i 23 {4 3 of the high speed relay is in its maximum displaced positions Since the control contacts 265 to 269 inclusive associated with low speed relay I82 are connected with an alternating voltage, phase shifting circuit these contacts are maintained separate from contacts H8, H9 and E2! which control the energization, of the saturating windings I31 and 13 of the saturable reactors IM- and I98 respectively. So far as the control of the saturable reactors use and 568 are concerned, the-contacts 63, i is" and 12!. operate exactly similar to the contacts H8, sand 52! respectively of Figur'e S. Except as described above all of the elements of Figure 9 are similar and operate" in the same manner as corresponding elements of Figure 8 and have been given the same-reference numerals.

System of Figures 1 0a and 1 0b the transmitting end-of the system, as in the previously described embodiments of the invention, this compensation-can be applied at'the receiving end of the system as shown in Figures 10a and 10b. In such a system the compensatingidevice along, with the compensating transformer 23 shown in Figurela is omitted. from the system as shownin Figure 10a. Otherwise, theelements shown in Figure 10a are exactly similar and function in the same manner as corresponding elements in Figure 1a and have been given the same reference characters. it will be noted that the series circuit including winding 12- on regulating transformer i! omits the compensating transformer winding 13 of Figure 1a and the :circuit including the winding 52 on regulating transformer. St omits the winding 53 of thecompensa ing transformer 23.

The receiving circuit of Figure lGbalso inclu"es the low speed receiver 26 and high speed eceiver Eiwhich have their various windings 'onnectsd to the transmittersof. thetransmitting uit and to the low speed and high speed relays 2 and 13s in exactly" the samemanner as 'escr bed' with reference to Figures 1a and'lb. The shaft Q? carrying the gears 96 and 93 which form part or" the drivinguconnection between the receivers andv 2?, however, carries an additional gear 2?; which drives a velocityand accel eration compensation device indicated? generally at-2i2. This device includes. a pivoted member 2'53 carried by a shaft 21 which. is concentric with the, shaft 3? and which enables the pivoted member 2% to rotate the. shaft 214' in either direction from aneutral'position shown in Figure 10b and Figure 11. The shaft 214 is returned to its neutral position by centering springs 216 and 2?? shown in Figure 11. The pivoted member 2T5 has shafts 2% and 2'19 journaled in it's-opposite ends, these shafts carrying gears 28]. and 282 respectively meshing with gear 21!. The shafts 278 and 219 also carry electrical conducting discs its 2%, respectively, passing between'the polesoi magnets 286 and 231 respectively, carried by, the pivoted member 273. The compensating device 212 operates in a manner very similar to the compensating device 22 of Figure la. That is to say, the drag on the discs 2'83 and285 caused by magnets 285 and 281 cause the pivoted member 213 to be carried by the gear 21! inthe direction of its rotation through an angle which is substantially directly proportional to the speed of rotation of thediscs 2 83' and ZB; Also the discs and 281 have consider-able moment of inertia; so. that an increase iniveloci'ty of the gea' r 2' causes the pivoted member 2V3 to be carried further in the direction of rotation of the gear 27! whereas a decrease in velocity causes the pivoted member 2.?3 to be carried in a direction opposite to the direction of rotation of the gear 27!.

Velocity and acceleration compensation is applied to the receiving system of Figure 1027 through variable resistance shown as comprising carbon piles E83 and 2239 connected in parallel with the carbon piles i and E55 associated with the high speed relay i3 5' and also in parallel with the contacts are, He and iii! of the low spee' relay 582. The carbon piles i5 3 and H53 difer entially excite the control solenoid windings E23 and [2d of a control solenoid which may be exactly similar to the control solenoid 2% of Figure 1? Direct current for energizing the control solenoid windings 523 and i2 3 is'derived from a --*-m n instead of applying velocity and acceleration to meet Cullen 233 mdudmg b dge res tifier circuit see, a transformer 2% and an alternating current source ihe carbon piles 23s and 23d of the compensator 272 also apply differential excitation to the coils 523, it, which diiferential excitation adds to orsubtracts from the carbon piles iii l' and 556 depending upon the velocity and acceleration conditions of the system. That is to say, a velocity in a given direction in th rotation of the system or increase in velocity increases the energization of the coil 23 or iii which already has the greatest excitation from the carbon piles 55 i and I55. A decrease in velocity has the opposite effect. Ihis applies greater power to the prime mover 23 of Figure 1c under high velocity or acceleration conditions and less power under conditions or" deceleration as explained with reference to Figures la and lb.

The system thus far described with reference to Figures 1011 and 102) may exhibit instability or tend to hunt and to correct this tendency, an anti-hunt generator 298, which may be driven by the shaft 89, may be provided to supply direct current energization for the various saturating windings of the saturable reactors Hill and Hal. This anti-hunt generator maybe a small direct current generator having an armature Winding 253s and a field winding 3%, the field winding being energized from the direct current source 29?; The direct current voltage of windmg '299 will be substantially proportional to the angular velocity of shaft so and will reverse in polarity upon reversing shaft 89. This voltage is supplied to the saturating winding of saturabie reactors l5! and I38 or It? and ids depending upon the polarity thereof, a pair of unidirectional conducted devices 302 and 303 being employed for this purpose. Thus, a voltage having polarity in one direction from armature 299 enables current flow from brush 36s of the genorator winding 2% through unidirectional conducting device 332, winding P58 of reactor it? and winding 13! of reactor m4 backto brush 306 of armature winding 299. Polarity in the opposite direction allows current flow from brush 386 of generator 298 through unidirectional conducting device 383, winding lbs of reactor [5i andwinding 136 of reactor H68 back to brush 3% of generator 298. In all cases the connectionis such that the anti-hunt generator 29% operates in opposition to the velocity compensation of device 252 by varying the impedance of the circuits of the windings on the relays Hi2 and 139'. The effect of the anti-hunt generator 293 is; however, less than that ofthe velocity compensating device 212 so "that the velocity compensating device 2212'- does supply effective velocity compensation. However, the employment of the anti-hunt generator 288 has been found to substantially eliminate any tendency for the system to oscillate or hunt.

The operation in Figures 10a and 10?) should be apparent from the description thereof. The velocity compensation device 212 increases the power delivered by the prime mover 28 shown in Figure 1b under conditions of high velocity in either direction in order to stiiien the system and cause the controlled member to more closely follow the control member even though the high velocity introduces additional friction load. Also, the compensation device 212 increases the power delivered by the prime mover under conditions of positive acceleration and decreases this power under conditions of negative acceleration to again stiffen the system against lags or overshooting caused by high inertia loads. The hydraulic system employed can be the same as that shown in Figure lb and has been omitted to avoid duplication in 10b. The anti-hunt generator 29.8 acts as a stabilizing means to effectively prevent hunting of the system when velocity and acceleration compensation is applied in the receiving end of the system and no retardation resistor 18!, such as shown in Figure 1?), is necessary in the system of Figure 102;.

The system of Figures 10a and 10b is particularly useful where the loads on different receivers connected to-the same transmitter are of different characteristics so that velocity and acceleration compensation is required for each individual set of receivers. compensator such as shown at 212 is employed with each set'of receivers. On the other hand, the system of Figures 1a and lband the various receiving systems, also discussed with reference to Figures 8 and 9, are particularly useful where a plurality of such receivers are; connected to the same transmitters to control loads having substantially the same characteristics. Under these conditions a single compensating device can be employed in the transmitting end of the system to compensate for all of the loads.

Figures 5 to '7 show a modified form of resistance control element 308 shown as being connected to a high speed control relay I39. The resistance element 388 has a roller contact 389 and such a resistance element can be substituted for the carbon piles employed with the high speed relays of Figures 119, 8 and 1012 as well as for the carbon piles 288 and 289 of Figure 11. In order that relatively wide changes in resistance can be effected by small movement of the spring element I52 the resistance element 308 may be wound on an insulating member 3H positioned at an angle to the axis of rotation of the contact roller 369 as shown most clearly in Figure 7. It will be apparent that if the angle between the member 3H and the axis 309 is made relatively small, large changes in resistance can be produced by relatively small movement of the roller 309.

While I have described the preferred embodiments of my invention, it is to 'be understood that the details thereof may be varied within the scope of the following claims.

I claim:

1. A self-synchronous system for maintaining a controlled device in substantial synchronism with a control device, said controlled device providing a friction load increasing with the speed of said controlled device and an acceleration load In such cases a varying with changes in speed of said controlled device, said system comprising, a self-synchronous transmitter having relatively rotatable members and means for producing an alternating field in said members, one of said members being driven by said control device, a variable speed power means for driving said controlled device, a self-synchronous receiver electrically connected to said transmitter and driven by said power means, means responsive to voltages resulting from an angle of disagreement between said receiver and said transmitter for controlling said power means to cause said controlled device to follow said control device, and compensator means, said compensator means including means responsive to the speed of said control device for rotating said magnetic field in said transmitter relative to said members to produce an efiective increase in said angle of disagreement to increase the power delivered by said power means to said controlled device in an amount substantially compensating for the increase of said friction load as the soeed of said devices increases, and means responsive to changes in speed of said control device for effectively varying said angle of disagreement to vary the power delivered by said power means to compensate for variations in said inertia load.

2. A self-synchronous system for maintaining a controlled device in substantial synchronism with a control device, said control device providing an inertia load varying with changes in speed of said controlled device, said system comprising, a self-synchronous transmitter having relatively rotatable members and means for producing an alternating field in said members, one of said members being driven by said control device, a variable speed power means for driving said controlled device, a self-synchronous receiver electrically connected to said transmitter and driven by said power means, means responsive to voltages resulting from an angle of disagreement between said receiver and said transmitter for controlling said power means to cause said controlled device to follow said control device, and compensator means, said compensator means including means responsive to changes in speed of said control device for rotating said magnetic field in said transmitter relative to said members to produce an eifective variation in said angle of disagreement to vary the power delivered by said power means to compensate for variations in said inertia load.

3. A self-synchronous system for maintaining a controlled device in substantial synchronism with a control device, said controlled device providing a friction load increasing with the speed of said controlled device and an inertia load varying with changes in speed of said controlled device, said system comprising, a self-synchronous transmitter driven from said control device, a variable speed power means for driving said controlled device, a self-synchronous receiver electrically connected to said transmitter, means actuated by said receiver for. supplying control voltages, control means responsive to said control voltages for controlling said power means to cause said controlled device to follow said control device, and compensator means, said compensator means including means responsive to the speed of one of said devices for varying the control voltages supplied to said control means to compensate for the increase of said friction load as the speed of said devices increases and means responsive to changes in speed of one of 

